Hydraulic cushion



Dec. 27, 1966 R. A. RASMUSSEN HYDRAULIC CUSHION 4 Sheets-Sheet 1 Filed sept. 1?. 1964 .mmm Q INVENTOR RASMUSSEN n .v v UL NR WN $1. W Q V A S@ W S mw.

BERT? @m BY @M @i W ATT-'YS ec. 27, i966 R. A. RAsMUssl-:N

HYDRAULIC CUSHION 4 Sheets-Sheet 2 Filed Sept. 17. 1964 /NVENTOR ROBERT A. RASML'JSSEN Dec. 27, 1966 R. A. RAsMussEN 3,294,388

HYDRAULIC CUSHION Filed Sept. 17, 1964 4 Sheets-Sheet 5 i Gfx/5 K yA TQMZO.,

O O O 0 0 O I i g ll INVENTOR ROBERT A. RASMUSSEN Dec. 27, 1966 R. A. RAsMUssEN 3,294,388

HYDRAULIC CUSHION Filed sept. 1T, 1964 4 sheets-sheet A '7T-l g- 16- /50 CAPACITY FORM FACTOR 2 3 OALLONS E XTENSIO N 5o" 4o" 3o" 20 FORM FACTOR .3 .5 1.75

INVENTOR ROBERT A. RSMUSSEN United States Patent O 3,294,388 HYDRAULIC CUSHIN Robert A. Rasmussen, @gden Dunes, Ind., assigner to Pullman Incorporated, Chicago, Ill., a corporation of Delaware Filed Sept. 17, 1964, Ser. No. 397,052 21 Claims. (Cl. 267-11) `My invention relates to improvements in hydraulic cushions, such as those used in railway cars for cushioning the lading against shock and impact forces.

Such a cushion comprises a cylinder closed at one end, and a piston which divides the cylinder into a high pressure chamber and a 1low pressure chamber, which are better referred to as the cushion chamber and the sump chamber respectively, since the pressure relationships are reversed on the out stroke.

The sump chamber is customarily sealed off by a flexible member, known as a boot, which extends from the open end of the cylinder to the piston rod so as to avoid the use of a sliding seal. The boot serves the secondary function of an expansible element so that the sump chamber can accommodate the fluid displaced by the volume of the piston rod when the cylinder is in its compressed position.

The volume characteristic of the boot, therefore, is that when the boot is in its axially contracted position it accommodates a greater volume of fluid than when it is in its axially extended position. For all practical pur- -poses it can be assumed that the volume of liquid enclosed by the boot in its axially extended position is negligible; it expands radially as it contracts.

The usual boot is a sleeve type boot which has not proved to be entirely satisfactory. An example is shown in Peterson Patent No. 3,035,827. One reason is that it is subjected to hoop stress due to the rolling or the folding of the sleeve `back on itself, and this tends to shorten the boot life, particularly in view of ozone and aging.

However, a more serious defect is encountered which is referred to as ballooning Under certain situations, the boot does not confine itself to its intended location within the cylinder overhang. Under certain pressure situations, the body of fluid enclosed within the boot causes the boot to be extended axially beyond the overhang, and the surge of the fluid in the unsupported fold of the boot causes the boot to expand radially beyond the overhang and interfere with the return spring (FIG. l2). Thus the boot may become pinched or perforated. It is believed that this situation is occasioned by a cavitation of the hydraulic iiuid within the cushion chamber. For example, the force exerted on the piston by the return spring may be of the order of from 15,000 to 20,000 pounds, representing a subatmospheric pressure within the cushion chamber which is considerably less than vapor pressure of the hydraulic fluid.

Irrespective of whether cavitation be the correct explanation of ballooning, the fact remains that the boot is called upon to accommodate a very substantial increase in fluid volume during the outstroke, and the increase is frequently in the form of a surge.

Thus, there are two conditions which must be recognized: the first condition is that the piston rod displacement must be accommodated during the in stroke, and secondly that the displacement due to cavitation or an equivalent phenomenon must be accommodated during the out stroke. The first condition is a necessary and desired function, but the second condition causes difficulties and hence is undesirable.

A third condition also occurs, namely, if a second impact occurs when the boot is in a ballooned condition Patented Dec. 27, 1966 during the out stroke surge, the boot may be cut olf by the cylinder overhang (FIG. 13).

It is an object of my invention to provide a hydraulic cushion which overcomes the above disadvantages of the prior art devices.

According to my invention, I provide a boot which is convoluted and which cooperates with the piston rod to provide a number of annular chambers, each, when in a partially extended position, having a capacity which is greater than that which is necessary to accommodate the volume of fluid represented by the piston displacement. Thus, at least a portion of the volume represented by the cavitation displacement can be accommodated by the convolution chambers without causing a stretching of the chamber wall which would cause interference with the springs or other parts of the cushion.

Another object of my invention is to provide an arrangement such that when stretching does occur, due to cavitation displacement, it will be confined to those convolution chambers which are disposed within the cylinder overhang.

Still another object is to provide an arrangement in which the convolution chambers are normally separated from each other under static conditions, but wherein communication can be established between adjacent charnbers by the development of a pressure differential to the end that a certain progressive pressure drop may be provided between the first and last convolution chambers during the out stroke. Thus pressure surges will tend to be dissipated over a measurable period of time.

An outstanding feature of my invention is that the body of liquid within the boot is split up into a number of small bodies of liquid so that there will be no surge of liquid from one end of the boot to the other.

A still further object of my invention is to provide a hydraulic cushion in which the boot will not be cut off or ruptured by a second impact.

Other objects, features and advantages of my invention will become apparent as the description proceeds.

With reference now to the drawings in which like reference numerals designate like parts:

FIG. l is a side view, partly in section, of a hydraulic cushion embodying my invention, the cushion being shown in its extended position',

FIG. 2 is a View similar to FIG. l but showing the cushion in its compressed position;

FIG. 3 is a right end View of FIG. 1;

FIG. 4 is an axial section of the convoluted boot prior to installation;

FIG. 5 is an enlarged fragmentary section showing one of the convolution chambers;

FIGS. 6 to 9 are sections taken along lines 6 to 9 inclusive of FIG. 4;

FIGS. l0 and 1l are diagrams illustrating the operation of my invention;

FIGS. 12 and 13 are diagrams representing the operation of the prior art device which embodies a sleeve type boot.

FIG. 14 shows a convolution chamber of FIG. 4 in a changed position representingmaximum capacity.

FIG. 15 is a sectional view taken along line 15-15 of FIG` 1 showing the static shape of a remote convolution during static condition;

FIG. 16 is a graph showing the relationship between chamber capacity and the form factor of the cross sectional area of the convolution chamber; and

FIG. 17 is a graph showing the capacity of the boot and piston rod displacement volume at different extension of the boot.

The hydraulic cushion 9, as shown in FIGS. 1 and 2, comprises as cylinder 10 closed at one end by a closed head 11. An open head 12 is located toward the remote end of the cylinder. Slidably mounted with the cylinder is a piston assembly 13. The latter comprises a piston proper 14 which is mounted on a hollow piston rod 15. The remote end of the piston rod 15 is closed by a plug 16. A pressure pad 17 is suitably secured to the piston rod and plug.

In order to avoid the use of a sliding seal between the piston rod 15 and the open head 12, a convoluted boot 18 is secured at one end to the open head 12 and at the other end to the remote end of the piston rod 15. Thus the boot 18 cooperates with the interior of the cylinder 10 to provide an enclosure for the hydraulic fluid.

Spring means 19 are provided to return the cushion to its extended position.

Ports 20 are provided in the hollow piston rod 15, as shown in FIGS. 1 and 2. In operation, as the hydraulic cushion is compressed, the movement of the piston 14 will cause the uid in the cushion chamber A (FIG. 10) ahead of the piston to pass through the ports 20 into the sump chamber B behind the piston which, as above indicated, is closed by the boot 18. The axial contraction of the boot 18 is accompanied by a radial expansion of the separate convolutions 21, 22 with the result that the displaced fluid, represented by the volume of the piston rod, is accommodated within the radially expanded boot.

In order to regulate the cushioning action of the device a metering pin 23 is provided which is suitably mounted at the front end on the closed head 11 and extends into the hollow piston rod 15. The metering pin is provided with grooves 24 which serve as orices to regulate the ow of uid, and preferably the grooves 24 are of a tapered configuration to provide a constant force-travel characteristic as described in Peterson Patent No. 3,035,714 granted May 22, 1962.

The proximate end of the boot 18 is secured to the open head 12 of the cylinder 10 by means of a clamp ring 25, aand a similar clamp ring 26 secures the remote end of the boot to the remote end of the piston rod 15.

A stop ange 27 on the piston rod 15 engages the open head 12 to limit outward movement of the piston assembly. In this FIG. 2 position, the proximate convolutions 21 are disposed within the cylinder overhang 28.

In order to permit more rapid return of the cushion, an out stroke check valve is provided. As shown in FIG. l, the piston 14 is provided with a plurality of ports 29 which are overlain at the front end by a valve ring 30. A suitable snap ring provides a stop for the valve ring 30. Thus considerable port area is available to hasten the out stroke of the piston to the left, but during the in stroke, the ports 29 are closed by the valve ring 30.

The separate convolutions include beads 33 which engage or hug the piston rod 15. Thus, a series of separate convolution chambers 31, 32 are provided, some of which (31) are proximate to the cylinder, and some of which (32) are remote. The boot 18, as shown in FIG. 4, is molded in its contracted form.

The capacity of the convolution chambers 31, 32 is variable, depending upon the height to width ratio of the axial cross section (form factor), and this in turn is determined by the axial extension of the boot. A comparison of FIGS. 4 and 14 illustrates this point, and this capacity relationship is plotted by curve 50 in FIG. 16. The maximum capacity corresponds to a form ifactor of 1/2 as shown in FIG. 14.

However, in extended position the volume of fluid accommodated due to piston rod displacement (piston rod displacement volume) is considerably less than the chamber capacity for that extension. Thus, due to atmospheric pressure, the chamber wall Will be pressed inwardly under static conditions as shown in FIG. 15. Here, the exterior of the boot is in the form of a number of separate rounded protuberances 53, arranged circumferentially. This can be referred to as the static shape of the convolution 21 as contrasted With the capacity shape which the chamber wall assumes when the boot is separated from the cushion as shown in FIGS. 4 and 6, for example.

The difference between piston rod displacement volume (curve 51) and capacity (curve 52) is plotted in FIG. 17 for different extensions. Thus, this difference between volume and capacity is available to accommodate the cavitation displacement volume without any stretching of the chamber wall.

Thus, assuming communication between the several convolution chambers 31, 32, and disregarding for the moment the matter of cavitation displacement, when the cushion is in its FIG. 1 extended position, the piston displacement volume is at a minimum, as shown by the curve 51 of FIG. 17. Then, as the cushion is compressed, the volume of uid in each chamber increases, but in each instance, the volume is considerably less than the capacity 52, until such time as the cushion is in its compressed position as shown in FIGS. 2, 4 and 5. Here the volume is substantially equal to the capacity. Then, during the out stroke the same conditions obtain. However, at all degrees of axial extension beyond the contracted position, the capacity is greater than the piston displacement volume. Thus, in the event that cavitation occurs, the cavitation displacement volume can be accommodated in the convolution chambers without such radial expansion as would interfere with the return springs 19. It will be particularly noted that due to the characteristics of the boot, the capacity increases with extension for more than onehalf of the extension. Since, during the out stroke, cavitation is accompanied by extension, the action is self compensating; the greater the amount of cavitation, the greater the capacity available to accommodate the cavitation displacement volume.

Since the increase in rate of cavitation volume is very rapid, in the nature of a surge, a feature of the present invention is that means are provided to absorb the surge so that the remote convolution chambers will not stretch radially in the event that the total displacement volume is materially in excess of the total chamber capacity. This feature is based on the fact that the convolution chambers are not in open communication with each other, due to the beads 33, with the result that the action is modified by a progressive pressure drop caused by a bead lifting phenomenon as 'hereinafter described.

As the piston moves from its extended FIG. 1 position into the compressed FIG. 2 position, the increased volume of fluid represented by the piston rod displacement will move through the passageway 34 between the open head 12 and the piston rod 15 into the rst convolution chamber 31, thereby tending to expand it. The capacity of the chamber is determined by the axial extension. However, as the pressure in the first convolution chamber 31 increases, it will lift up the bead 33 to provide communication between the rst and second convolution chamber, thus permitting a certain amount of uid to ow from the rst to the second, and equalizing the pressure therebetween.

This bead lifting occurs progressively all the way down the line from the proximate convolution chambers 31 to the remote convolution chambers 32, and each bead lifting phenomenon in elfect represents a pressure drop. Furthermore the progressive bead lifting is believed to occupy a measureable amount of time. As a result, an instantaneous pressure surge transmitted to the rst convolution chamber will be absorbed or dissipated over a measurable amount of time, such as a fraction of a second, due to the progressive bead lifting phenomenon, and furthermore, the pressure in the last convolution chamber will be considerably less than the pressure in the first convolution chamber at this time.

As shown in FIG. 4, the peripheral wall area of the proximate convolution chambers is greater than the wall area of the remote convolution chambers. Thus, less unit pressure is required to lift the beads of the proximate chambers'31 than in the case of the remote chambers 32. Preferably, this reduction in chamber size or wall area is progressive, there being four groups of chambers of each diameter. This size relationship also facilitates the bleeding of the remote chambers 32 during the latter part of the out stroke where the chambers have been filled to capacity by cavitation.

Another feature of the present arrangement is that due to the progressive pressure drop from one chamber to the next, the major increase in chamber volume will occur in the proximate convolution chambers 31, and these are at all times located within the cylinder overhang, even when the cushion is in its fully extended position. Thus, even though stretching may occur in the proximate chambers 31, it is not likely to occur in the remote convolution chambers 32, and it will not cause interference with the return spring 19.

I have found it desirable to mitigate the bead lifting pressure drop between the first few proximate convolution chambers 31. This is accomplished, as shown in FIG. 4 and FIGS. 6 to 9, by providing ports, in the form of grooves 35 made in the beads 33. In order to maintain a degree of progressive action, the port area is decreased from the first to the fifth convolution chamber 31, and this is diagrammatically shown by the use of four ports between first and second chambers, three between the second and third chambers, two between the third and fourth, and one between the fourth and fifth. This arrangement has been found to be satisfactory in avoiding such an abrupt radial expansion or stretching of the first convolution chamber 31 as would cause it to engage the cylinder overhang 28 prior to the time that bead lifting occurs.

FIGS. and 11 diagrammatically compare the positions of the parts in the static and in the cavitation positions, respectively. The bodies of fluid 41 and 42 of FIG. 10 represent the piston rod displacement volume in each of the separate convolution chambers 31, 32. However, when cavitation occurs, as indicated by the void 40 in FIG. 11, the cavitation displacement volume is represented by the enlarged fluid bodies 41 and 42.

FIG. 12 is a diagram similar to FIG. 11 but showing the prior art device 43 at the same instant. The sleeve type boot is not shown, but the reference numeral 44 designates the body of uid within the sleeve type boot. The rate of the out stroke movement in FIG. 12 as well as in FIG. ll is sufficiently high, due to the formation of the void 40, as to cause the flow of fluid through the passageway 34 to be in the form of a surge (wavy arrow 4S) which, in the Case of the sleeve type boot device of FIG. 12 causes the elongation and ballooning of the boot represented by the portion 45 of the body of fluid which extends beyond the overhang 23. Thus the ballooned portion 45 will interfere with the return springs which surround the overhang and piston assembly. In the case of a somewhat slower out stroke, the ballooned portion 45 would appear only on the under half of the body of fluid 44, in which the ballooning would be more of a gravitational effect than of a surge effect.

FIG. 13 shows the relationship of the parts of the prior art device 43 at the instant of a second impact. In other words, if, during the early out stroke instant of FIG. 12, the car is bumped in a direction to cause inward displacement of the cylinder 10', represented by the arrow 46, the cylinder overhang 28' would cut off the ballooned portion 45. In other words, the ballooned portion 45 tends to remain stationary due to inertia. The extremely high pressure developed by the second impact causes collapse of the cavitation void 40, but the pressure relationships cause the formation of a second cavitation void 47 in the sump chamber B. The fluid cannot move out of the boot into the sump chamber B sufficiently fast as to reduce the volume of the body of fluid 44, or to prevent the formation of the cavitation void 47.

Essentially the same result would occur if the second impact were in the opposite direction, resulting in an inward displacement of the piston assembly with respect to the body 44 which tends to remain stationary due to inertia. Here, the ballooned portion 45 would be pinched between the pressure pad 15' and the cylinder overhang 2S. In either case, the sudden application of pressure causes a very rapid relative movement of the parts with respect to the body of Huid 44 which, as above mentioned, tends to remain stationary due to inertia.

Aside from the fact that stretching or radial expansion of the boot beyond the cylinder overhang does not occur in my invention, the second impact pinching effect is eliminated for the reason that the convolutions of the boot splits up the liquid into a number of small bodies 41 and 42. By virtue of this arrangement, there will be no surging of the liquid in an axial direction from one end of the boot to the other due to the rapidity of the out stroke, or due to any other cause.

In the preferred embodiment of my invention shown, the over all length of the boot in its relaxed and contracted position as shown in FIG. 4, and not including the end flanges 25 and 26', is substantially 20 inches; in its extended position of FIG. 1, the length is substantially 50 inches.

There are fourteen convolutions, the space between the beads 33 being 1% inches. In the axial cross section, the width of the convolution chambers is substantially 1 inch, and the height of the proximate convolution chambers 31 is substantially 2 inches, and the height of the remote convolution chambers 22 is substantially 11/2 inches. The diameter of the piston rod 15 is substantially 4 inches; this also is the inner diameter of the boot at the beads 33, and the outer diameter ranges from 8% inches at the proximate end to 7% inches at the remote end. The wall thickness is 1/8 inch. When in contracted position, the capacity of of the boot is 2 gallons. The volume of liquid when in the extended position of FIG. 1 is half a gallon, as shown in FIG. 17, although this fact is not particularly important because it is not a design parameter. The net volume of fiuid displaced by the piston rod is 1% gallons.

Although the outer diameter of the boot shown is substantially twice the piston rod diameter, there can be a considerable variation in this ratio without materially affecting the relationships shown in FIG. 16. Similarly, the boot in its fully extended position could more nearly approximate the total wall length of the boot, thus giving a lower form factor in extended position, without adversely affecting the operation. In order to obtain full advantage of the variable capacity feature, the boot design preferably is such that when in extended position, the form factor will be somewhat less than .5 which represents maximum capacity, and that when in contracted position, the form factor should be somewhat greater than 1. In the embodiment shown, the contracted position form factor of the proximate chambers 31 is 11%6, and of the remote chambers 32 is 1%5, with an average of 1.75. The total wall length of the boot is between 3 and 31/2 times the axial length of the boot when in contracted position.

The form factor for the various extensions can best be determined when the boot is separated from the cushion as shown in FIG. 4.

FIG. 5 indicates that when in contracted position, the volume of liquid accommodated can slightly exceed the capacity under very slight pressures, that is, under pressures which are insuflicient to cause radical expansion or stretching of the convolution.

Substantially the same relationships as shown in FIG. 17 prevail if the last two proximate convolutions of the boot are cut off so that the length of the boot (not counting the iianges 25 and 26') is about 17" in its relaxed or molded position. As a result, in the contracted position, which corresponds to a 20" extension, the form factor is somewhat less. Thus, the volume relationships are substantially the same as shown in FIG. 17.

Although I have shown only a preferred embodiment of my invention herein it will be understood that various modifications and changes may be made in the construction shown without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A hydraulic cushion comprising a cylinder having a closed head at one end and being open at the other end, a piston slidably mounted within said cylinder, a piston rod for said piston extending through said open end, means providing communication between opposite sides of said piston, and a convoluted boot having one end secured to said cylinder and the other end secured to the remote end of said piston rod, said boot having a plurality of beads closely surrounding said piston rod and providing, when in axially contracted position, a plurality of convolution chambers to accommodate the uid displaced by said piston rod when said hydraulic cushion is in its contracted position.

2. In a hydraulic cushion comprising a cylinder having a closed head at one end and an open head at the other end, a piston slidably mounted within said cylinder and dividing same into a cushion chamber and a sump chamber, a piston rod for said piston extending through said open head, and means providing communication between said cushion chamber and said sump chamber, the improvement which comprises a convoluted boot closing olf said sump chamber and having a plurality of beads closely surrounding said piston rod and providing a plurality of convolution chambers, said convolution chambers being of variable capacity depending on the extension of said boot, and the maximum capacity of said chambers occurring at an extension of between 50% and 100% extension.

3. In a hydraulic cushion comprising a cylinder having a closed head at one end and an open head and an overhang at the other end, a piston slidably mounted within said cylinder and dividing same into a cushion chamber and a sump chamber, a piston rod for said piston extending through said open head, means providing communication between said cushion chamber and said sump chamber, the improvement which comprises a convoluted boot closing off said sump chamber and having a plurality of beads closely surrounding said piston rod and providing a plurality of convolution chambers, said boot when in contracted condition being substantially twice the diameter of said piston rod and being wholly received within said overhang.

4, A hydraulic cushion comprising a cylinder having a closed head at one end and being open at the other end, a piston slidably mounted within said cylinder and dividing same into a cushion chamber and a sump chamber,

` a piston rod for said piston extending through said open end, means providing communication between said cushion chamber and said sump chamber, and a boot closing oi said sump chamber, said boot being a convoluted boot having a plurality of beads engaging said piston rod and providing, when in axially contracted position, a plurality of convolution chambers, said convolution chambers forming a part of said sump chamber to accommodate the uid displaced by said piston rod when said hydraulic cushion is in its contracted position.

5. A hydraulic cushion as claimed in claim 4 in which the outer diameter of the boot when in contracted position is substantially twice the diameter of said piston rod.

6. A hydraulic cushion as claimed in claim 4 in which the axial length of said boot when in extended position is more than twice the length of said boot when in contracted position.

7. A hydraulic cushion as claimed in claim 4 in which the wall length of said convoluted boot is substantially three times the axial length of said boot when in contracted position.

8. A hydraulic cushion as claimed in claim 4 in which the form factor of said convolution chambers when in contracted position is substantially 1.75 to 1.

9. A hydraulic cushion as claimed in claim 4 in which the form factor of said convolution chambers when in extended position is substantially less than 1 to 2.

10. A hydraulic cushion as claimed in claim 4 in which said convolution chambers have a variable capacity depending upon the extension of said boot, the form factor of said convolution chambers being greater than 1 when in contracted position and being less than 1/2 when in fully extended position.

11. A hydraulic cushion as claimed in claim 4 which includes port means extending between the first and second convolution chambers which are closest to said piston.

12. A hydraulic cushion as claimed in claim 4 which includes port means providing communication between a series of proximate convolution chambers which are closer to said piston than the others.

13. A hydraulic cushion as claimed in claim 12 in which the port area of said port means decreases as one moves away from that proximate chamber which is closest to said piston.

' 14. A hydraulic cushion as claimed in claim 4 in which said cylinder includes an overhang, port means providing communication between a series of proximate convolution chambers which are closest to said piston, all of said intercommunicating proximate convolution chambers being located within said overhang when said cushion is extended.

15. A hydraulic cushion as claimed in claim 4 in which the convolution chambers proximate to said open end are of larger outer diameter than the convolution chambers which are remote from said open end, and port means providing communication between a plurality of said proximate convolution chambers.

16. A convoluted boot for use in a hydraulic cushion comprising a plurality of convolutions which are separated by beads, the convolutions at one end of said boot having a greater outer diameter than the convolutions at the other end of said boot.

17. A convoluted boot as claimed in claim 16 in which the form factor of said larger convolutions is substantially 2, and in which the form factor of said smaller convolutions is substantially 1.5.

18. A convoluted boot as claimed in claim 16 which includes notches formed in the beads associated with said larger convolutions.

19. A convoluted boot for use in a hydraulic cushion comprising a plurality of convolutions which are separated by beads, the diameter of the convolutions at one end 0f said boot being substantially two times the inner diameter of said beads, and the diameter of the convolutions at the other end of said boot being substantially 1.8 times the inner diameter of said beads.

20. A hydraulic cushion comprising a cylinder having a closed head at one end and being open at the other end, a piston slidably mounted within said cylinder and dividing same into a cushion chamber and a sump chamber, a hollow piston rod for said piston extending through said open end, means providing communication between said cushion chamber and said sump chamber, a boot closing off said sump chamber, and an out stroke check valve bypassing said orice and effective to permit iiuid flow only during the outer stroke of said piston assembly, said boot being a convoluted boot having a plurality of beads engaging said piston rod and providing, when in axially contracted position, a plurality of convolution chambers, said convolution chambers forming a part of said sump chamber to accommodate the fluid displaced by said piston rod when said hydraulic cushion is in its contracted position.

21. A hydraulic cushion comprising a cylinder having a closed head at one end and being open at the other end, a piston slidably mounted within said cylinder and dividing same into a cushion chamber and a sump chamber, a hollow piston rod for said piston extending through said open head. a boot closing off said sump chamber, a metering pin mounted at one end on said closed head and extending through said piston and into said hollow piston rod, the space between the surface of said metering pin and said piston defining an orifice providing communication between said cushion chamber and said sump chamber, and controlling the rate of the in stroke of said piston, and an out stroke check valve by-passing said orifice and effective to permit Huid ilow only during the out stroke of said piston assembly, said boot being a convoluted boot having a plurality of beads engaging said piston r-od and providing, when in axially contracted position, a plurality of convolution chambers, said convolution chambers forming a part of said sump chamber to accommodate the uid displaced by said piston rod when said hydraulic cushion is in its compressed position.

References Cited by the Examiner UNITED STATES PATENTS 3,150,866 9/1964 Peterson 267-1 FOREIGN PATENTS 897,293 5/ 1962 Great Britain.

10 ARTHUR L. LA POINT, Primary Examiner.

R. M. WHOLFARTH, Assistant Examiner. 

1. A HYDRAULIC CUSHION COMPRISING A CYLINDER HAVING A CLOSED HEAD AT ONE END AND BEING OPEN AT THE OTHER END, A PISTON SLIDABLY MOUNTED WITHIN SAID CYLINDER, A PISTON ROD FOR SAID PISTON EXTENDING THROUGH SAID OPEN END, MEANS PROVIDING COMMUNICATION BETWEEN OPPOSITE SIDES OF SAID PISTON, AND A CONVOLUTED BOOT HAVING ONE END SECURED TO SAID CYLINDER AND THE OTHER END SECURED TO THE REMOTE END OF SAID PISTON ROD, SAID BOOT HAVING A PLURALITY OF BEADS CLOSELY SURROUNDING SAID PISTON ROD AND PROVIDING, WHEN IN AXIALLY CONTRACTED POSITION, A PLURALITY OF CONVOLUTION CHAMBERS TO ACCOMMODATE THE FLUID DISPLACED BY SAID PISTON ROW WHEN SAID HYDRAULIC CUSHION IS IN ITS CONTRACTED POSITION. 